Degradation of Current Gain for Ion Implanted 4H-SiC Bipolar Junction Transistor
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1195-B08-04
Degradation of Current Gain for Ion Implanted 4H-SiC Bipolar Junction Transistor Yuki Watabe, Taku Tajima and T. Nakamura Dept. of Electronics, Electrical and Computer Engineering, Hosei University Koganei, Tokyo 184-8584, Japan Tel:+81-42-387-5104 Email:[email protected] ABSTRACT Degradation of current gain for ion implanted 4H-SiC bipolar junction transistor is described. The influence of bandgap-narrowing to the collector and base currents of the transistor was investigated using ISE-TCAD simulator. Simulated results show good agreement with the measured results, which show that the common emitter current gain of 3.9 is obtained at a maximum base concentration of 2 × 1017 /cm3 and a maximum emitter concentration of 4 × 1019 /cm3 for ion implanted 4H-SiC BJTs. INTRODUCTION SiC is a promising wide-bandgap material for high power and high temperature devices because of the high breakdown strength and thermal conductivity. SiC BJTs are usually fabricated using double or triple mesa-etching of epitaxial layers on SiC substrate [1]-[2]. On the other hand, SiC BJTs with ion implanted emitter has been reported that shows the low current gain, which is attributed to the low minority carrier life-time in the base-emitter space charge region [3] due to crystal damages and surface roughness by ion implantation. In this structure, the current gain decreases due to the influence of bandgap-narrowing for the heavily doped emitter and base regions, which affect the reliability of the devices because the large collector and base currents flow the surface region. To improve it by using excellent annealing method, we reported superior characteristics of 4H-SiC BJTs devices with fabricating only ion implantation techniques [4]. However, in the low injection level of Gummel plots, the ideality factors of the base current (IB) and collector current (IC) were estimated to be 2 and 1.5, respectively because of recombination current in the space charge region between the base and emitter and in the surface of surrounding the emitter region. It was found that the base current mainly flew the surface of surrounding the emitter region and the small collector current flew in the intrinsic base region because of surface recombination [4]. In this paper, we analyze the degradation of the current gain of ion implanted SiC BJTs using ISE-TCAD simulator. We also demonstrate the influence of bandgap-narrowing on the base and collector current and the current gain. EXPERIMENT Device structure Figure 1 schematically illustrates the structure of triple ion implanted 4H-SiC BJTs. The width of intrinsic base was 300 nm. The both depths of base contact region and emitter region were 500 nm.
Figure 2 shows the doping profiles of the base, base contact, and emitter regions, which were calculated by using the stopping and range of ions in the matter (SRIM) simulation. The maximum base and emitter concentration were 2 × 1017 and 4 × 1019 /cm3, respectively. The maximum base contact concentration was 4 × 1019 /cm3. Fabrication
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